Low-temperature vapor phase epitaxial systems are known for producing thin layers of semiconducting silicon-germanium alloy. Such layers can be used by the semiconductor processing industry to expand the range of applications currently available to silicon. Addition of silicon-germanium layers to silicon technology permits operation of silicon-like integrated circuits at faster speeds than are attainable by silicon circuits themselves. In addition, silicon-germanium layers are sensitive to light at wavelengths used by modem fiber-optic networks, silicon layers are not. This means that photonic detectors made from silicon-germanium layers could be used at these wavelengths (1.1 .mu.&lt;.lambda.&lt;1.9 .mu.m). The inherit compatibility of silicon-germanium layers with silicon processing technology thus enables silicon-like circuits to be used in conjunction with modem fiber-optic network systems, a capability that is not possible with silicon-only circuits today. Improvements are desired in the operation and flexibility of a machine capable of producing high quality silicon-germanium layers for use in the electronics and opto-electronics industries. The process of depositing single-crystal layers of silicon and silicon-germanium from gaseous sources at low temperature (.about.500.degree. C.) was pioneered by Meyerson at IBM in the mid-to-late 1980's; see B. S. Meyerson; Low-Temperature Silicon Epoxy by Ultrahigh Vacuum/Chemical Vapor Deposition; Appl. Phys. Lett. 48 (12) 24 March 1986. As a result of this work, IBM has cooperated with Leybold A. G. who now produces a commercial ultra-high vacuum chemical vapor deposition system based on the IBM design. The only other commercial system of this type known to the author is manufactured by Vactronic, lnc. (Bohemia N.Y.).
It is desirable to provide a vapor phase epitaxial deposition system that has a very efficient and thorough toxic gas purging mechanism, in view of the extremely toxic nature of the source, or process, gases introduced into the reactor furnace, for producing the thin epitaxial layers upon the silicon wafers positioned therein. It is also highly desirable to rapidly detect the slightest leak of the highly toxic gases before such a leak can become dangerous to the health of operating personnel. Finally, even minute leaks in the gas distribution system can lead to unacceptably high levels of contamination in the resulting silicon-germanium layers.
It is also deemed desirable to readily counteract any potential deviation in the proper ratios of two or more source gases to be simultaneously introduced into the reactor furnace, which deviation could result in undesirable changes in the composition of the epitaxial films being deposited.